Film badge dosimeter
Encyclopedia
The film badge dosimeter, or film badge, is a dosimeter
used for monitoring cumulative exposure
to ionizing radiation
. The badge consists of two parts: photographic film
, and a holder. The film is removed and developed to measure exposure.
extends the dynamic range
to several orders of magnitude. Wide dynamic range is highly desirable as it allows measurement of very large accidental exposures without degrading sensitivity to more usual low level exposure.
, such that only the target radiation is monitored. To monitor gamma ray
s or x-ray
s, the filters are metal
, usually tin
or lead
. To monitor beta particle emission
, the filters use various densities of plastic
. It is typical for a single badge to contain a series of filters of different thicknesses and of different materials, the precise choice may be determined by the environment to be monitored. The use of several different thicknesses allows an estimation of the energy/wavelength of the incident radiation.
Filters are usually placed on both the back and front of the holder, to ensure operation regardless of orientation. Additionally, the filters need to be sufficiently large (typically 5 mm or more) to minimize the effect of radiation incident at oblique angles causing exposure of the film under an adjacent filter. This places a minimum useful size on the holder and badge.
Under special circumstances, where an operator may receive a high dose to one area of the body (e.g. the hands of a radiopharmacist) then additional monitoring of the area is required. For monitoring of hands, a miniature Thermoluminescent Dosimeter
worn as a finger ring is usually used.
The film badge is not widely used in the USA
, having been replaced by multi-chip thermoluminescent dosimetry
. However, the FBD is the dominant dosimeter used in the rest of the world.
Dosimeter
Dosimeters measure an individual's or an object'sexposure to something in the environment — particularly to a hazard inflicting cumulative impact over long periods of time, or over a lifetime...
used for monitoring cumulative exposure
Radiation poisoning
Acute radiation syndrome also known as radiation poisoning, radiation sickness or radiation toxicity, is a constellation of health effects which occur within several months of exposure to high amounts of ionizing radiation...
to ionizing radiation
Ionizing radiation
Ionizing radiation is radiation composed of particles that individually have sufficient energy to remove an electron from an atom or molecule. This ionization produces free radicals, which are atoms or molecules containing unpaired electrons...
. The badge consists of two parts: photographic film
Photographic film
Photographic film is a sheet of plastic coated with an emulsion containing light-sensitive silver halide salts with variable crystal sizes that determine the sensitivity, contrast and resolution of the film...
, and a holder. The film is removed and developed to measure exposure.
Description
The film is sensitive to radiation and, once developed, exposed areas increase in optical density (i.e. blacken) in response to incident radiation. One badge may contain several films of different sensitivities or, more usually, a single film with multiple emulsion coatings. The combination of a low-sensitivity and high-sensitivity emulsionEmulsion
An emulsion is a mixture of two or more liquids that are normally immiscible . Emulsions are part of a more general class of two-phase systems of matter called colloids. Although the terms colloid and emulsion are sometimes used interchangeably, emulsion is used when both the dispersed and the...
extends the dynamic range
Dynamic range
Dynamic range, abbreviated DR or DNR, is the ratio between the largest and smallest possible values of a changeable quantity, such as in sound and light. It is measured as a ratio, or as a base-10 or base-2 logarithmic value.-Dynamic range and human perception:The human senses of sight and...
to several orders of magnitude. Wide dynamic range is highly desirable as it allows measurement of very large accidental exposures without degrading sensitivity to more usual low level exposure.
Holder
The holder may contain a number of filters that attenuate certain types of radiationRadiation
In physics, radiation is a process in which energetic particles or energetic waves travel through a medium or space. There are two distinct types of radiation; ionizing and non-ionizing...
, such that only the target radiation is monitored. To monitor gamma ray
Gamma ray
Gamma radiation, also known as gamma rays or hyphenated as gamma-rays and denoted as γ, is electromagnetic radiation of high frequency . Gamma rays are usually naturally produced on Earth by decay of high energy states in atomic nuclei...
s or x-ray
X-ray
X-radiation is a form of electromagnetic radiation. X-rays have a wavelength in the range of 0.01 to 10 nanometers, corresponding to frequencies in the range 30 petahertz to 30 exahertz and energies in the range 120 eV to 120 keV. They are shorter in wavelength than UV rays and longer than gamma...
s, the filters are metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...
, usually tin
Tin
Tin is a chemical element with the symbol Sn and atomic number 50. It is a main group metal in group 14 of the periodic table. Tin shows chemical similarity to both neighboring group 14 elements, germanium and lead and has two possible oxidation states, +2 and the slightly more stable +4...
or lead
Lead
Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...
. To monitor beta particle emission
Beta decay
In nuclear physics, beta decay is a type of radioactive decay in which a beta particle is emitted from an atom. There are two types of beta decay: beta minus and beta plus. In the case of beta decay that produces an electron emission, it is referred to as beta minus , while in the case of a...
, the filters use various densities of plastic
Plastic
A plastic material is any of a wide range of synthetic or semi-synthetic organic solids used in the manufacture of industrial products. Plastics are typically polymers of high molecular mass, and may contain other substances to improve performance and/or reduce production costs...
. It is typical for a single badge to contain a series of filters of different thicknesses and of different materials, the precise choice may be determined by the environment to be monitored. The use of several different thicknesses allows an estimation of the energy/wavelength of the incident radiation.
Filters are usually placed on both the back and front of the holder, to ensure operation regardless of orientation. Additionally, the filters need to be sufficiently large (typically 5 mm or more) to minimize the effect of radiation incident at oblique angles causing exposure of the film under an adjacent filter. This places a minimum useful size on the holder and badge.
Usage
The badge is typically worn on the outside of clothing, around the chest or torso. This location monitors exposure of most vital organs and represents the bulk of body mass. The badge is worn over the protection to monitor the dose actually received to unprotected parts (parts not covered with lead, etc).Under special circumstances, where an operator may receive a high dose to one area of the body (e.g. the hands of a radiopharmacist) then additional monitoring of the area is required. For monitoring of hands, a miniature Thermoluminescent Dosimeter
Thermoluminescent Dosimeter
A thermoluminescent dosimeter, or TLD, is a type of radiation dosimeter. A TLD measures ionizing radiation exposure by measuring the amount of visible light emitted from a crystal in the detector when the crystal is heated. The amount of light emitted is dependent upon the radiation exposure...
worn as a finger ring is usually used.
The film badge is not widely used in the USA
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...
, having been replaced by multi-chip thermoluminescent dosimetry
Thermoluminescent Dosimeter
A thermoluminescent dosimeter, or TLD, is a type of radiation dosimeter. A TLD measures ionizing radiation exposure by measuring the amount of visible light emitted from a crystal in the detector when the crystal is heated. The amount of light emitted is dependent upon the radiation exposure...
. However, the FBD is the dominant dosimeter used in the rest of the world.
Advantages
The film badge has several advantages over other types of dosimetry:- Permanent record of exposure: The developed film is physical evidence of the radiation exposure. The film can be stored after developing and reading, and could be reviewed at a later date if there is a query over exposure.
- Exposure pattern discrimination: A film badge offers limited discrimination between different patterns of exposure. A single exposure tends to leave sharp shadows on the film from the filters, whereas multiple small exposures at different angles will leave a rim of blurring around the filters. This may allow the linking of a dose with a specific incident and provides a degree of protection against tampering (e.g. deliberate exposure to a radiation source).
- Radiation type detection: Use of multiple filters allows separate measurement of beta and gamma exposure, and estimation of energy spectra. Additional filters can be added to detect neutron radiation (e.g. cadmium). The sensitivity of film to low energy (< 20 keV) gamma or x-radiation can be better than electronic dosimeters.